Cylinder spacers are used to achieve proper deck height when using stroker crankshafts and/or longer connecting rods. Using spacers is one accepted method to lower CR and works very well on VW engines. Compression Ratio Recommendations; GB 801-CR, GB 801-DECK and GB 801-HEADS are mandatory reading. Additional adjustments can be made with our stackable metal barrel shims.
Do not use paper gaskets for sealing under the barrels with or without shims/spacers. Seal only with high temperature RTV silicone sealer, such as GB 9000B. Install a small bead of GB 9000B against the cylinder diameter and the cylinder flat surface (spacer or shim if any) so it seals the cylinder to the spacer or shim (if any) to the case all together. Be clear that this must only be done at final assembly just before the heads are to be torqued.
How to calculate the approximate spacer and/or shim amount when the stroke is changed: Subtract original stroke from new stroke in mm, then multiply by 0.0197. This gives spacer measurement in thousandths of an inch. Remember this is only if case height, rods and new stroke are exact. Whenever possible check deck height first by a trial assembly, or order additional shims to space out cylinders as necessary.
Never run less than 0.040" (1mm) deck clearance with quality crankshaft and rods. Poor quality cranks, rods, and/or line bored cases often require up to 0.060" deck to clear in race applications. Always allow 0.050" to 0.060" deck clearance on street engines. I have run a deck clearance of as much as 0.250" to lower compression with no adverse affects, however the heads should always be Semi-Hemi cut first. How to mathematically calculate deck: